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Re: [PATCH v4 1/5] sim: cgen: add remainder functions (needed for OR1K lf.rem.[sd])


On 2017-09-01 00:33, Stafford Horne wrote:
I can't tell for sure because I'm not maintainer of sim/, but I suppose that we would need a proper implementation that doesn't use the host fpu here.

Right, as mentioned in the summary, this is the one place that is a bit
controversial.

I was thinking its kind of strange to not allow using libmath, since
integer math runs on the host system, why not FPU as well?
(probably to implement this I would just copy from libmath in the end:)

That was just my conclusion after reading the comment in sim-fpu.h:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=sim/common/sim-fpu.h;h=d27d80a513aa8d996a7b4c6af53fde31dcb8dad7;hb=HEAD#l54

It is easy for floating point unit implementations to return wrong or slightly different results. Integer math is more consistent.

https://sourceware.org/git/?p=glibc.git;a=blob_plain;f=sysdeps/ieee754/dbl-64/e_remainder.c;hb=HEAD

There are actually no OpenRISC cores that implement the remainder
instruction (as its a bit complicated to do in hardware and not really used much). I could remove it if the implementation is beyond the scope of this
series.

Indeed, it can always be contributed later.

Simon


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